Conventional coating systems can be found, for example, in electrochemical oxygen sensors in which a ceramic body produced from a solid electrolyte is provided with at least one electrode exposed to a gas to be analyzed, and a porous overcoat covering the electrode. The electrode is made up of a catalytically active material such as platinum which is capable of adjusting the equilibrium setting of the gas to be analyzed on the electrode surface.
U.S. Pat. No. 4,199,425 describes a sensor in which an additional catalytic material, rhodium, is introduced into the pores of the porous overcoat by impregnation and subsequent calcination. The rhodium precipitates onto the pore walls of the entire overcoat in the form of ultra-fine particles so that no specific coating thickness can be set in the porous overcoat.
A method for the currentless deposition of metals onto metallic surfaces and the monitoring of these processes is described in British Patent No. 2 198 750. However, this method does not make the specific application of a metallic coating onto an electrode surface through a porous protective coating possible.